This invention relates to an hydraulic distributor of the kind used in hydraulic systems for controlling, for example, hydraulic motors or jacks.
Such an hydraulic distributor has a distributing slide that is movable through several positions. This distributor is described as the proportional type when, for a given displacement of the slide, a given constant output is obtained in the operating circuits independent of the conditions of force or couple encountered by the receiver, jack, or similar equipment. Such a proportional hydraulic distributor is disclosed, for example, in the application for French Pat. No. 84 06 747, made by the present Applicant on the 18th Apr., 1984 under the title: "Hydraulic Distributor of the Proportional Type with Sensing of the Highest Pressures in the Operating Circuits." U.S. patent application Ser. No. 724,523 corresponds to such application for French patent. Besides the main distributing slide, an hydraulic distributor according to the present invention includes a pressure compensating slide which moves against a compression spring in a bore provided with annular operating channels, each one is connected to various branches of the hydraulic circuit.
In practice, it will be seen that, even if the position of the compensating slide is established at any moment in time by an equilibrium between the return force of the spring and the forces due to pressures which are applied to it at each of its ends, parasitic phenomena occur in dynamic operation which harm the stability of the control. These parasitic phenomena are due essentially to the appearance of a force of hydrodynamic drag, which is connected with the instantaneous characteristics of the flow, and which acts on the compensating slide with an intensity proportional to the variation in the quantity of movement between the upflow and downflow portions of the flow within the slide.